Rearrangements or deletions of chromosome 17 are some of the most frequently observed changes identified in breast, brain, colon, lung, and ovarian tumors. Molecular analyses show that in addition to the BRCA1 gene on 17q21 and the TP53 gene on 17p13.1 there is at least one other tumor suppressor gene on chromosome 17 involved in the pathogenesis of these diseases. Regions of loss of heterozygosity (LOH) identified on 17p13.3, occur frequently in ovarian tumors that express wild-type TP53 and BRCA1. From their preliminary studies of ovarian cancer, we have identified a common region of allelic loss on 17p13.3, that spans less than 40 kilobase pairs. Using positional cloning methods, they have recently identified a previously unreported gene, which they provisionally refer to as OVCA1 (Ovarian Cancer 1 gene), that maps to this critical region. Northern blot analysis reveals that OVCA1 mRNA is expressed in normal surface epithelial cells of the ovary, but the level of the transcript is significantly reduced or is undetectable in the majority of the ovarian tumors and tumor cell lines examined. High stringency blots revealed strongly hybridizing restriction fragments in tissue from all species examined, indicating a highly conserved cellular function. OVCA1 shares significant amino acid sequence identity when compared to proteins from yeast and nematode. The investigators propose to evaluate the potential role of OVCA1 in the development of ovarian cancers by 1) determining the frequency at which mutations occur in this gene in an extensive panel of ovarian tumors using Single Strand Conformation Polymorphism (SSCP), direct sequencing, and In Vitro Synthesized Protein (IVSP) assays, and 2) evaluating its ability to suppress clonal out- growth when introduced by transfection into tumor cell lines that express reduced levels of OVCA1. Since this locus may also be involved in breast cancer, they will perform mutational analyses on a large panel of breast tumors as well. They will also initiate studies to determine the function of OVCA1 by establishing the subcellular location of this protein using either antibodies generated against GST-OVCA1 fusion proteins or epitope tagged proteins and by identifying potentially important protein interactions by far-Western blot and immunoprecipitation analyses. In addition, newly identified polymorphic simple tandem repeat (STR) markers, which are intragenic to OVCA1, may be used to directly evaluate the frequency at which allelic loss is observed in other tumors in our panel, such as brain, cervical, endometrial, and lung. Overall, these studies should provide important insights into some of the specific genetic abnormalities involved in the pathogenesis of sporadic breast and ovarian cancer and increase the understanding of the basic biology of these diseases with ultimate clinical benefits.